only problem with implementing that is that a lot of students would be failing due to their own carelessness and then salty parents would blame all the teachers and get them fired
Easy solution, Have the students sign a contract to use their phones in class without any repercussions from the teacher. This way the teacher won't get fired as the student willingly made the choice with evidence proving so.
while that is a great idea, it'd probably require a parent signature as well, assuming the students are under 18. and lots of parents might not be willing to go along with it